Well, we do have to keep the 18-ability limit for abilities gained through leveling. Also the fact that every melee needs to have combos (as opposed to Rets which had only Crusader Strike/Divine Storm/Exorcism and Shaman with Lava Lash/Stormstrike/Maelstrom Weapon procs).
Off-heals are a given on RDM; it is, after all, the original hybrid of the FF series and there's ways to implement heals into the job without making it overpowered. Make the heals inconvenient to cast and present risk to the RDM and you'd force them to make a decision. If you tie it to a proc (see my suggestion in my sig), even better because then you're including the choice between dealing magic damage or using the proc to heal someone.
Buffs are limited, partly because SE decided to blend stat buffs into party bonuses (because they want to encourage party diversity). Otherwise I could also see RDMs having stuff along the lines of old school Blessing of Might or Strength of Earth totem. Granted, in the current game it'd make RDM required unless you gave other jobs the ability to provide those stat buffs as well. On the other hand, I wouldn't want RDM to be there only because of buffs or some other gimmick like it was in FFXI.
If you're thinking of stuff like Seal of Light/Judgment of Light (which healed party members that attacked the mob with the debuff), the old blessings (Protection, Sacrifice, Sanctuary) or even really crazy stuff like Divine Intervention, I'll admit that's going a bit too far.